Betaines Structures

Demethylvasconine (85) (9-methoxy-5-methyl-phenanthridin-8-olate) presented in Scheme 31 was found in Crinum kirkii (95P1291) (Amaryllidaceae). Although published as cation, no information about the anion of this alkaloid is given. Its relationship to other alkaloids of this class, however, makes a betainic structure more than likely and this is confirmed by a comparison of the NMR data of 85 with the cationic and betainic alkaloids presented in Table III. This betaine is isoconjugate with the 2-methylphenanthrene anion and thus defined the alkaloid as a member of class 1 (odd alternant hydrocarbon anions). Whereas substitution of the isoconjugate phenanthridinium moiety at the 1-position with an anionic fragment results in zwitterions (cf. Section III.D), the phenanthridinium-2-olate is a mesomeric betaine. 

The hydrazone structure 40 can be eliminated at once many examples of this class of compounds are known and their properties are completely different from the diaziridines. For example, 3,3-dimethyldiaziridine has a heat of combustion of about 35 kcal higher than the isomeric acetone hydrazone. Further pairs of isomers of diaziridines and hydrazones are known. The spectrum eliminates both the hydrazone structure and the betaine structure 41. The diaziridines do not absorb in the UV range. In the infrared spectrum, absorption is completely absent in the double-bond region. - The NMR spectrum of 3,3-dimethyldiaziridine is in agreement with a formulation that has two equivalent iV-protons. ... 

The 1-methoxy-compound " is not formed, but rather 7-methyl guanosine (32b), with a betaine structured - "... 

Most of the reported 1,2,5,6-tetrazocine systems probably do not exist in the monocyclic form but rather as the tetraazapentalene betaine structure (see Introduction) 2 3 7"13 for the tetra-phenyl-substituted system, the compound does actually exist as the mesoionic tetraphenyl-[1,2.3]triazolo[l,2-h][l,2,3]triazole, as determined by H and 13C NMR spectroscopy.15 The following syntheses arc therefore questionable. 

When the neutral macrocycles [64] were dissolved in solvents other than water, equilibria between the neutral forms and betaine structures were also found. In ethanol, the equilibrium between a phenol and a betainic... 

The amine opens the THF ring system because of a nucleophilic attack at the a-C atom of the coordinated THF. Owing to the movement of a proton from the ethyl to the amide group with simultaneous ethene elimination, a betaine structure appears. 

Mesomeric betaine structure 7, which is a rough simplification of the real situation indescribable by a single structure, represents another degree of saturation. The real structure of mesomeric betaines is a resonance hybrid of several dipolar structures <1977T3203>. Additional unsymmetrical substitution or aza substitution increases the number of possible distinct dipolar structures. 

Acyclic boryloxyalkylphosphines with tricoordinated phosphorus and boron are capable of forming cyclic betaine structures with four-coordinated P and B atoms. The ability to be converted into a more stable four-coordinated state accounts for many chemical transformations of boryloxyalkylphosphines. Diphenylboryloxymethyl(methyl) phenylphosphine (92) readily disproportionates to give 1,3,2,5-dioxabora-taphosphoniarinane (103). [Eq. (60)] (83IZV2541). Similar interaction is... 

Isolation of intermediate 119 appeared to be impossible, since the formation of a more stable betaine structure (120) was observed. The interaction of compound (120) with a second molecule of boric acid ester in the presence of triethylamine or pyridine gave rise to spirobicycle 121 [Eq. (79)]. 

The disulfide fragment separating phosphorus and boron atoms was not replaced in 181 by chloral even after refluxing in benzene, evidence for high betaine stability. In methylene chloride, 175 reacts with 1,2-naphthoquinone, yielding phosphorane 182 [Eq. (135)]. This result is surprising, as one could have expected the formation of a betaine structure. 

It follows from the above X-ray data that betaines I and II have some structural peculiarities. Two main peculiarities are especially pronounced for betaines I. These compounds have the sterically strained gauche-conformation of the main chain due to the intramolecular Coulomb interaction of the cationic and anionic centers and noticeable distortions of the bond lengths in it. In Section 5 we discuss how these peculiarities of the betaine structure reflect their reactivity. 

Pyran-4-one (56a) and its benzo derivative (chromone) show chemical properties in agreement with substantial jr-electron delocalization and consistent with a betaine structure 56b (Scheme 27). Experimental data have therefore generated numerous theoretical studies on the aromaticity of pyranones, which have been extensively reviewed.219 Earlier studies suggested that chemical shifts and coupling constants... 

The chemical behavior of thiabenzene derivatives is in agreement with an aromatic character. 1,2,4,6-Triphenylthiabenzene has a betainic structure 175a,b (Scheme 69).223 Benzofusion or substitution with... 

Efforts to add Lewis acids to dialkyliminoboranes R BNR were not so successful, aa would be expected, since betaine structures of the type R B=NR—A with an unfavorable linear sextet boron atom would be formed (19, 33). Equation (26) is restricted to iminoboranes XBNR with a 7i-electron donating group X. 

FischeH as a bisphenylazo compound (415), whereas Bamberger et al. advocated the equivalent (416) of a betaine structure. A cyclic betaine structure was later support d on the basis of its spectroscopic properties. Cogent arguments for the representation of dehydro-dithizone as a meso-ionic heterocycle (413, R> = = Ph) were... 

A betainic structure is very effective in decreasing 17eff according to the LeBlanc s proposal for the TCNQ anion radical salt (eq. 1), where a is the molecular polarizability of the cation and r is the distance between TCNQ anion radical and a cation [67] ... 

The IR spectra of aromatic quinolizinium derivatives have been used in the usual way to learn the nature of substituents. The classical example was its use by Woodward et al. (49JA379) to demonstrate the betaine structure of sempervirine (Scheme 2). Another important use in the aromatic series has been in establishing as identical the products of two different preparations of a quinolizinium derivative when, due to decomposition on heating, the usual melting point criteria are unreliable. 

C NMR data in support of the betaine structure of the diazaborolidine 56 indicate that delocalization of the positive charge causes a downfield shift for C-5 (ca. 13 ppm) and C-3a/C-6a (ca. 4 ppm) <2004CC1860>. 

Diazoxine, a red product which accompanies the formation of 8-methoxy-quinoline from 8-hydroxyquinoline and diazomethane, was first encountered by Caronna and Sansone in 1939. Later, it was suggested that the properties of this product were consistent with structure 189 (R = Me, R = R = H). ° Subsequently, this product has been prepared by treatment of the iodide 190 with potassium carbonate, and the betaine structure has been confirmed by spectroscopic and chemical studies. Compound 189 (R = Me, R = R = H) is isolated as hydrated violet-red needles. The UV and visible spectra are strongly dependent on the nature of the solvent the colors of solutions vary from yellow to blue. Bromination gives the 5,7-dibromo derivative (189 R = Me, R = R = Br), which is also obtained from... 

The bright red betaines 269 form salts with dilute hydrochloric acid and are dealkylated by hot ethanolic potassium hydroxide. The mesomeric betaine structure (269) is fully supported by spectroscopic properties. ... 

Oxidation of the alkaloid lycorine (359) gives a red, hygroscopic solid which readily forms salts with mineral acids. This product, which has been assigned the betaine structure 358, has also been obtained from Ungernia minor and named ungeremine. . zss TV-methyl derivative (357 R = Me, R R = OCH2O) has also been described. ... 

Corresponding to the type of surfactant the hydrophobic group consists of an anion (anionics), a cation (cationics) or segment in nonionic or related polymer surfactants. Also, in amphoteric surfactants or betaine structures the fluorocarbon tail is extremely hydrophobic. 

The position of the carbonyl group in the IR spectra of various pyranones and pyridones, etc., is indicative of the C-0 bond order, and therefore of the importance of the betaine structure. However, this criterion must be used with caution because of the non-localized nature of the vibrations just mentioned. 

Complete aromaticity in coumarin (19), isocoumarin (28) and 3H- 2- benzopyran-3-one (206) can only be realized if the O—CO function contributes two electrons to form a 1077-electron system, which would necessarily possess a betaine structure. 

The basicity of pyran-4-one, which is significantly greater than that of simple aromatic and aliphatic ketones, is apparent from its pKa of 0.1 and has been rationalized in terms of a betaine structure (212 X = O). Benzo-fusion increases the basicity the p2sTaof chromone (20) is 2.0 (65ZOB1707). As a result of their basicity, both pyran-4-one and chromone have a great propensity to form salts with acids (63CJC505). 

If pyran-4-one is a 677-electron aromatic system, it must adopt the betaine structure (212 X = 0), which would exhibit a large dipole moment. The observed moment for (18) is 3.7 D. A dipole moment of 1.9 D is obtained by vector summation of bond and group moments. Clearly, if mesomeric effects were absent, the difference between the calculated and observed moments would be very small. The magnitude of the observed dipole moment suggests there is considerable it- electron delocalization in pyran-4-one. However, the calculated value for the betaine structure (212 X = 0) is 21 D (73MI22203) and thus it appears that the extent of delocalization is, after all, quite small. 

In order to obtain further insight into the 7r- electron distribution in these molecules and the possible involvement of betaine structures, a dipole moment study was undertaken (76JHC609). However, the results did not enable any firm conclusions to be drawn. 

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